This invention relates to a liquid-phase epoxidation process using a non-zeolitic, supported niobium oxide catalyst to produce epoxides from hydrogen peroxide and olefins. Surprisingly, the supported niobium oxide catalyst is active in liquid-phase epoxidation.
Many different methods for the preparation of epoxides have been developed. Generally, epoxides are formed by the reaction of an olefin with an oxidizing agent in the presence of a catalyst. The production of propylene oxide from propylene and an organic hydroperoxide, such as ethyl benzene hydroperoxide or tert-butyl hydroperoxide, is commercially practiced technology. This process is performed in the presence of a solubilized molybdenum catalyst, see U.S. Pat. No. 3,351,635, or a heterogeneous titania on silica catalyst, see U.S. Pat. No. 4,367,342. Another commercially practiced technology is the direct epoxidation of ethylene to ethylene oxide by reaction with oxygen over a silver catalyst.
Much current research is conducted in the direct epoxidation of olefins with oxygen and hydrogen. For example, JP 4-352771 discloses the formation of propylene oxide from propylene, oxygen, and hydrogen using a catalyst containing a Group VIII metal such as palladium on a crystalline titanosilicate. The Group VIII metal is believed to promote the reaction of oxygen and hydrogen to form an in situ oxidizing agent. U.S. Pat. No. 5,859,265 discloses a catalyst in which a platinum metal, selected from Ru, Rh, Pd, Os, Ir and Pt, is supported on a titanium or vanadium silicalite. Other direct epoxidation catalyst examples include gold supported on titanosilicates, see for example PCT Intl. Appl. WO 98/00413.
Besides oxygen and alkyl hydroperoxides, another oxidizing agent useful for the preparation of epoxides is hydrogen peroxide. U.S. Pat. No. 4,833,260, for example, discloses olefin epoxidation using hydrogen peroxide and a titanium silicate zeolite. U.S. Pat. No. 5,679,749 discloses the epoxidation of olefins with hydrogen peroxide in the presence of a crystalline siliceous molecular sieve zeolite wherein niobium is isomorphously substituted for silica in the framework. One drawback of these processes is the expense of the titanium and niobium zeolites.
In sum, new processes for the epoxidation of olefins using hydrogen peroxide are needed. I have discovered an effective, convenient epoxidation process that gives good productivity and selectivity to epoxide.
The invention is an olefin epoxidation process that comprises reacting an olefin and hydrogen peroxide in a solvent in the presence of a non-zeolitic, supported niobium oxide catalyst. The supported niobium oxide catalyst is surprisingly useful in the epoxidation of olefins with hydrogen peroxide.